This invention concerns radio transmitters and, more particularly, mobile or portable type radio transmitters, such as the currently popular Citizens Band or "CB" radio units in which the antenna is frequently connected and disconnected from the unit. A problem is inherent in the design of these units, inasmuch as if the transmitter is attempted to be operated when the antenna has been inadvertently left unconnected to the transmitter output stage, overload of the output stage of the transmitter will occur, due to the absence of an external load, i.e. the antenna, to absorb the power of the transmitter output stage causing failure of the components. While protective circuitry has in the past been incorporated in communication devices, the relatively low price of these units has precluded the inclusion of any such protective devices in "CB" units. Thus, many of the millions of units in the field have become casualties to this inadvertence by the operator to properly connect his antenna to the transmitter unit prior to operation.
It is an object of the present invention to provide a device for preventing such damage from occurring due to operation of the transmitter unit with the antenna uncoupled.
It is a further object of the present invention to provide a device for preventing such damage which device is readily installed on existing transmitter units without necessitating the use of special tools or rewiring of the unit.
It is a still further object of the present invention to provide such a device which is relatively low in cost and adaptable to such low cost devices as the cheaper "CB" units.
It is yet another object of the present invention to provide such a device which provides the operator with an indication of the fact of the antenna being uncoupled from the transmitter unit upon attempted operation of the "CB" unit, which indication is provided without the need for an external power source.